Exposure to the human polyomaviruses JCV, BKV and ASV usually occurs during childhood and generally results in a subclinical infection. These viruses may persist in the kidney, and in the case of JCV, may go on to cause the fatal demyelinating brain disease, PML. A number of naturally occurring polyomaviruses have been isolated which differ biologically from the prototype viruses. Among these difference are the types of tumors they induce in animals and the frequency with which they transform cells in vitro and cause tumors in vivo. A number of findings emphasize the importance of investigating the oncogenic potential of JCV, BKV and ASV in humans: i) BKV and JCV are highly tumorigenic in rodents, and JCV is the first human virus to cause solid tumors in primates, ii) cells within PML lesions resemble malignant astrocytes of glioblastomas, iii) gliomas have been found in close proximity of PML lesions, iv) some tumors induced in animals by these viruses closely resemble those commonly found in people and v) members of this family of viruses (e.g. papilloma, polyoma) cause benign and/or malignant tumors in their natural hosts. The long term objectives are to i) investigate the oncogenic potential of new human polyomaviruses, ii) identify the factors contributing to their transforming activity, and iii) determine the role of specific regulatory sequences in the lytic and oncogenic behavior of these viruses. Questions addressed by the specific aims include: 1) Is the strain of JCV that circulates in the human population substantially different from the currently studied strain isolated from diseased brain tissue? Does "kidney" JCV adapt to growth in glial cells, and does adaptation play a role in the pathogenicity and oncogenicity of the virus? 2) What is the biological significance of the hypervariability of polyomaviral regulatory sequences? Can sequence alterations be correlated with phenotypic differences? 3) What is the molecular basis for the inefficient transforming activity of JCV? 4) Are recently discovered human polyomaviruses significantly different from prototypes JCV and BKV in their oncogenic behavior? Do these viruses have an etiological role in human cancer? To approach these questions a number of molecular techniques will be employed, e.g. S1 analysis of early viral mRNAs, sequence analysis of variant regulatory regions, synthetic oligonucleotide mutagenesis, CAT assays, and transfections with r-DNAs.